The present invention relates generally to the field of electric protective devices, such as for providing overload protection for motors and other loads.
In the field of electrical protective devices, a range of devices are known and are presently in use in various combinations. For example, in a typical arrangement for applying power to a load, such as an electric motor, the circuitry may include fuses, circuit breakers, thermal overload tripping devices, contactors, and so forth. In a typical application, the components are selected and assembled based upon the current ratings and other operating parameters of the load. For example, motor protective circuitry is typically selected based upon the motor full load current rating. A thermal overload device may be selected to provide tripping at a first level, such as 6 to 10 times the full load of current rating, with faster, higher current tripping being provided by an electromagnetic device, such as a circuit breaker.
While such arrangements provide adequate protection for loads, they are not without drawbacks. For example, many separate and differently rated components are generally provided and associated with one another in various combinations, depending upon the nature and rating of the load. Little effort has been made in the field for reducing the number of components or the number of product offering by extending the ratings of the components and circuits. There is a need, however, in the field for product offerings that can service a range of loads, such as motors of different sizes, while providing both thermal and instantaneous trip performance for larger loads, and smaller loads equally. Such products are not currently available on the market.